Process for the recovery of high purity benzene



2,885,454 PROCESS FOR THE RECOVERY CF' HIGH PURITY BENZENE Filed oct. 28, 1955 May 5, 1959 H. E. cil-:R z-:TALV

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H.'E.'c1ER -ET AL PROCESS FOR'THEI4 RECOVERY OF HIGH PURITY EENZENE Filed 001;. 28, '1955 2 Sheets-Sheet 2 $02 fie-M0 VA L BBL. L. 06 H6) 7.99 BEL. (783 BBL. 66 H6] PRODUT LEF//VS REMOVAL /67 BBL. 06 H6) ATTORNEY.

OLEF/NS 25 BEL.

IN V EN TORS Harry E. C/er, Math/s T. Waddell,

PRUCESS FOR THE RECOVERY' 0F HIGH PURITY BENZENE Harry 1E. Cier and Mathis T. Waddell, `Baytown, Tex., assignors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, ENJ., a corporation of Delaware Application Uctober 28, 1955, Serial No.v543,310 4 Claims. (Cl. 260-674) This invention relates to a process for the recovery of high purity benzene. More particularly, this invention relates to a process for recovering substantially pure benzene from a benzene-containing mixture of hydrocarbons.

The present invention may be briefly described as a method for recovering benzene from a feed stock comprising a mixture of benzene with naphthenic and paraflinic hydrocarbons containing 6 and 7 carbon atoms, and preferably boiling in the range of about 115 to about 220 F. wherein such feed stock is fractionated to provide an overheads fraction boiling below about 145 F., a first distillate (i.e., side stream) fraction boiling in the range between about 145 and about 170 F., a second distillate (i.e., side stream) fraction boiling in the range between about 170 and about 180 F. and a bottoms fraction boiling above about` 180 F.; wherein said lirst side stream fraction is contacted with liquefied sulfur dioxide in an extraction zone under conditions to form a first extract stream `and a first raflinate stream; wherein said second side stream fraction is dissolved in liquefied sulfur dioxide and the thus prepared solution is contacted with a wash oil comprising non-aromatic hydrocarbons boiling substantially above about 180 F. under conditions to form a second raffinate stream and a second extract stream, wherein sulfur dioxide is removed from said extract streams and wherein said sulfur dioxide-free extract streams are fractionated in combination to provide an overhead fraction and a bottoms fraction consisting of at least about 95 weight percent of benzene.

Hydrocarbon feed stocks boiling in the range of about 115 to about 220 F. and containing about 5 to about 15 volume percent of benzene are employed as starting materials in accordance with the present invention. Feed stocks of this nature may be obtained, for example, from Virgin naphthas, catalytically dehydrogenated (eg, hydroformed) naphthenic hydrocarbons, etc. Such feed stocks normally comprise mixtures of aromatic, paratlinic and naphthenic hydrocarbons containing six and seven carbon atoms. Minor amounts of olenic hydrocarbons may also be present in some instances. The naphthenic and parainic hydrocarbons present in feed stocks of this character comprise compounds such as n-hexane, cyclohexane, methyl cyclopentane, dimethyl pentanes, etc. which form azeotropes with benzene which boil over a comparatively wide range. As a consequence, the benzene is not readily recovered from such mixtures by distillation.

It has been discovered in accordance with the present invention that a fraction of such a feed stock boiling within the range of about 145 to about 170 F. will contain, as compared with the original feed, an enhanced amount (e.g., 15 to 25 volume percent) of benzene and that such fraction, when contacted with lqueed sulfur dioxide under extraction conditions wherein extract and raffinate phases are formed, will provide an extract stream containing a still further enhanced amount (e.g.,

atesj Patent' about 40 to 60 volume percent) of benzene; the nonbenzene components of such extract being of a nature such that they may be removed as overheads upon sub sequent azeotropic distillation.

It has further been discovered that a fraction of the feed stock boiling within the range of about 170 to about 180 F. will comprise from about 40 to 70 volume percent of benzene and that the amount of benzene contained in such fraction may be substantially enhanced by dissolving the fraction in liquefied sulfur dioxide and countercurrently contacting the resultant solution with a wash oil comprising non-aromatic hydrocarbon boiling substantially above 180 F. under conditions to form extract and raffinate phases; the extract phase containing recoverable benzene. A suitable wash oil may corn prise, for example, a mixture of paraflinic and naphthenic hydrocarbons boiling in the'range of about 400 to about 650 F.

In accordance with the present invention, sulfur dioxide is removed from the two above-described extract streams and the sulfur dioxide free extracts are then distilled in combination to provide an overheads fraction containing substantially all of the impurities, and a bottoms fraction consisting of at least about volume percent of benzene. In many situations the feed stock may contain a minor amount of oleiinic hydrocarbons not removable by distillation or extraction with liquefied sulfur dioxide and in this situation the high purity benzene bottoms fraction will contain a minor amount (e.`g., about l to about 4 volume percent) of such olefins. In this situation, olens may be removed from the bottoms fraction by any conventional means such as sulfuric acid treatment, clay contacting, etc., whereby there is 'obtained a product containing a still higher concentration of benzene.

The present invention may also be considered in connection with the accompanying drawings wherein:

Fig. 1 diagrammatically illustrates a preferred method for recovering benzene in accordance with the present invention; and

Fig. 2 is a diagrammatic iiow sheet which is further descriptive of the process of the present invention.

Referring now to Fig. 1, the numeral 10 designates a charge line for supplying a benzene-containing Vfeed stock boiling within the range o-f about to about 220 F. and preferably free from pentanes to a suitable fractionating means such as a tirst distillation zone 12. The distillation zone 12 may comprise a plurality of fractional distillation towers but, in the interest of simplicity, has been shown as a simple distillation tower. It will be understood that the distillation zone 12 will include the necessary auxiliary equipment necessary for proper dis tillation such as suitable vapor-liquid contacting means, bell cap trays, etc. for insuring intimate liquid-vapor contact. Means may also be provided for inducing reflux. Suitable temperature control means such as a steam coil 13 is also provided.

Within the distillation zone 12 the feed stock is separated into an overheads fraction 14 boiling below about F., a first side stream fraction discharged through a side line 16 and boiling within the range of about 145 yto about F.; a second side stream fraction discharged through a side line 18 and boiling Within the range of about 170 to about 180 F.; and a bottoms fraction boiling above about F. which is discharged through a bottoms line 20.

In accordance with the present invention the first and second side stream fractions are separately treated in order to recover the benzene contained therein.

The lirst side stream fraction isfed by the line 16 to a suitable extraction Zone 22 and liquefied sulfur dioxide `is simultaneously charged to the extraction zone 22' through a charge line 24 for countercurrent contract with the first side stream fraction under conditions to form an extract phase and a raffinate phase. About 11/2 to about 3 volumes of liquefied sulfur dioxide per volume of side stream fraction may be used for this purpose. The raffinate phase is discharged overhead through a line 26 and the first extract phase is discharged as bottoms through a line 28.

The second side stream fraction discharged from the distillation zone 12 through the line 18 is dissolved in liquefied sulfur dioxide in any suitable manner such as, for example, by simultaneously charging the second side stream fraction through the line 18 and liquefied sulfur dioxide through a line 30 to a suitable baflfe type incorporator 32. An appropriate amount of liquefied sulfur dioxide, up to about 21/2 volumes of liquefied sulfur dioxide per volume of side stream fraction may be used for this purpose; the amount of sulfur dioxide employed being sufficient to form a single phase solution of the side stream fraction in the liquefied sulfur dioxide. The thus formed solution is passed from the incorporator 32 by way of a line 34 to a point adjacent the top of a wash tower 36. At the same time a wash oil comprising paraffinic and naphthenic hydrocarbons boiling substantially above 1807 F. (c g., a paraffinic and naphthenic hydrocarbon fraction boiling in the range of about 400 to 650 F.) is charged to the wash tower 36 adjacent the 'bottom thereof by a line 38 under conditions to form a second raffinate phase and a second extract phase. From about to 20 volumes of wash oil per volume of solution may be used for this purpose. The second raffinate phase is discharged overhead from the wash tower through a line 40 and the second extract phase is discharged from the wash tower 36 through a bottoms line 42.

Sulfur dioxide is removed from the first and second extract streams and the extract streams are distilled in combination to provide a high purity benzene bottoms fraction. If desired, the first and second extract streams may be separately treated for removal of the sulfur dioxide and then combined for distillation. However, in the interest of economy it is preferable to combine the extract streams prior to sulfur dioxide removal, whereby the sulfur dioxide removal and distillation operations are conducted with the combined stream. A preferred manner in which this may be accomplished is as follows:

The first extract phase in the line 28 and the second extract phase in the line 42 may be simultaneously charged to a feed line 44 leading to a suitable stripping means 46 wherein liquefied sulfur dioxide contained in the combined extract is volatilized for overheads removal through a line 48. As a result, there is discharged from the bottom of the stripper 46 through a line 50 an extract stream substantially free from sulfur dioxide. The thus treated extract stream is charged by way of the line 50 to a second distillation zone 52 which is similar to the distillation zone 12 and which may comprise a plurality of distillation towers. The charge material is distilled in the zone 52 under suitable temperature and pressure with a reux condition and preferably with reffux in the refiux ratio of about 5 to 1 to about l5 to 1 in order to provide an overheads fraction discharged by way of the line 54 comprising not more than about 30% of the feed material charged to the distillation zone 52. The overheads fraction withdrawn through line 54 contains naphthenic and paraffinic hydrocarbons not removed from the first and second extracting steps and a minor amount (c g., volume percent) of benzene. The bottoms fraction discharged by line 56 may be recovered as product. When a feed stock is employed containing a minor amount of olefins, as is frequently the case, substantially all of the impurities will be of an olefinic nature. In this situation it is generally preferable to further purify the bottoms fraction by removal of the olefinic contaminants. This may be accomplished, for example, by closing the valve 58 in line 56 and by charging the material in the line 56 through a line 60 controlled `by a valve 62 to an olefins removal zone 64. Olefins may be removed in the zone 64 by any of the suitable processes known to those skilled in the art such as sulfuric acid treatment, clay contacting, etc. whereby there is obtained a product containing an enhanced amount (i.e., at least about 99 volume percent) of benzene which is discharged from the zone 64 through a line 66. By-product material is discharged from the zone 64 through a line 68.

The first and second raffinate streams discharged through the lines 26 and 40 will normally contain at least a minor amount of benzene and, if desired, one or both of the raffinate streams may be treated for the removal of sulfur dioxide and then recycled, whereby the benzene contained therein will ultimately be recovered.

Thus, for example, the first raffinate stream may be charged by way of the line 26 to a suitable sulfur dioxide removing means such as a stripper 70 wherein the sulfur dioxide is volatilized for overheads discharge through a line 72 to provide a sulfur dioxide-free raffinate stream discharged through a line 74 controlled by a valve 76. If the thus treated raffinate stream is not to be recycled, the valve 76 may be opened so that the stream may be discarded from the system. If the material is to be recycled, however, the valve 76 is closed and the raffinate stream is routed by way of a line 78 controlled by a valve 80 to a recycle line 82 leading to the feed stock charge line 10 for the distillation zone 12.

The second raffinate stream discharged from the wash tower 36 through the line 40 may be fed by way of a line 84 controlled by a valve 86 to the line 26 leading to the stripper 70 for treatment along with the first raffinate stream. However, it will sometimes happen that the first extract stream is to be discarded while the second extract stream is to be recycled, or that the first raffinate stream is to be recycled, while the second raffinate stream is not. Accordingly, and as an alternative, the second raffinate stream contained in the lin: 40 may be charged by Way of a lire 88 controlled by :t valve 90 to a suitable sulfur dioxide removal means sucli as a stripper 92. Within the stripper 92 the sulfur dioxide contained in the second raffinati.l stream is volatilized for discharge through an overheads line 94 to provide a sulfur dioxide-free raffinate stream discharged from the stripper 92 through a bottoms line 96 controlled by a valve 98. If the second raffinate stream is to be discarded from the system the valve 98 is opened. However, if the sulfur dioxide-free second raffinate stream is to be recycled, the valve 98 is closed and a valve 100 in a second raffinate recycle line 102 is opened whereby the material will be charged to the recycle line 82 leading to the feed stock charge line 10.

The overheads fraction from the distillation zone 52 which is discharged by the line 54 will also normally contain benzene and, if desired, this fraction may also be recycled. If the overheads fraction 54 is not to be recycled, the valve 55 is opened whereas, if the material is to be recycled, the valve 55 is closed whereby the overheads fraction will be charged to the recycle line 82 leading to the feed stock charge line 10 for the first distillation zone 12.

The present invention may also be considered in connection with the following example which is given by way of illustration and not as a limitation on the scope of this invention.

EXAMPLE 1 A feed stock boiling within the range of about to about 220 F. is obtained by the hydroforming of a naphthenic hydrocarbon material, such a feed stock having the composition set forth in Table I.

The feed stock is fractionated to provide an overheads fraction boiling below about 145 F., a bottoms fraction boiling above about 180 F., a first side stream fraction boiling within the range of about 145 to 170 F. and a second side stream fraction boiling within the range of about 170 to about 180 F.

The rst side stream fraction will have a composition as set forth in Table I (fraction (2)) and the second side stream fraction Will have a composition as set forth in Table I (fraction (3)).

With reference to Fig. 2 and considering the situation wherein 10,000 barrels of a feed stock having a composition set forth in Table I is fractionated; there is obtained an overheads fraction comprising about 1,200 barrels and substantially free from benzene, a first side stream fraction of about 2,700 barrels containing about 493 barrels of benzene, a second side stream fraction of about 700 barrels containing about 465 barrels of benzene, and a bottoms fraction of about 5,400 barrels containing about 52 barrels of benzene.

The rst side stream fraction is extracted with liqueed sulfur dioxide under conditions to provide a rst extract stream and a first ranate stream. The first raffinate stream may comprise -about 1,930 .barrels of hydrocarbon material and contain about 38 barrels of benzene. The iirst extract stream may comprise about 770 barrels of hydrocarbon material and contain about 455 barrels of benzene.

The second side stream is dissolved in sulfur dioxide and the solution is countercurrently contacted with a wash oil under conditions to form a second extract phase and a second raiinate phase. The second rainate phase may comprise about 280 barrels of hydrocarbon material and contain about 170 barrels of benzene. The second extract stream may comprise about 420 barrels of hydrocarbon material and contain about 395 barrels of benzene.

The lirst and second extract streams are combined and sulfur dioxide is removed therefrom to provide a combined stream containing about 1190 barrels of hydrocarbon material in which about 850 barrels will be benzene.

The combined stream is then fractionated to provide an overheads stream containing hydrocarbons lighter than benzene which azeotrope with benzene and a bottoms fraction consisting of at least about 96 volume percent of benzene and olenic contaminants. The overheads fraction may contain about 375 barrels of hydrocarbon material of which about 67 barrels will be benzene. The bottoms fraction may comprise about 815 barrels of hydrocarbon material and contain about 783 barrels of benzene.

The bottoms fraction is then treated for the removal of oleins whereby about 25 barrels of contaminants will be removed to provide about 790 barrels of benzene of about 99% purity.

Having thus described our invention, what is claimed is:

1. A method for recovering benzene from a feed stock comprising a mixture of benzene with six and seven carbon atom paraftnic and naphthenic hydrocarbons which comprises the steps of fractionating said feed stock to provide a rst overheads fraction boiling below about 145 F., a rst distillate fraction boiling in the range between about 145 and about 170 F., a second distillate fraction boiling in the range between about 170 and about 180 F. and a rst bottoms fraction boiling above about 180 F., countercurrently contacting said lirst distillate fraction solely with liquefied sulfur dioxide in an extraction zone under conditions to form a lirst extract phase and a rst rarlnate phase, dissolving said second distillate fraction in liquefied sulfur dioxide, countercu-rrently contacting said thus prepared solution of said second distillate fraction with a wash oil comprising non-aromatic hydrocarbons boiling substantially above about 180 F. under conditions to form a second extract stream and a second raii'inate stream, removing sulfur dioxide from said first and second extract stream and fractionating said extraction streams in combination to provide a second overheads fraction and a second bottoms fraction consisting of at least about weight percent of benzene, said feed stock containing not more than a minor amount of olens.

2. A method as in claim 1 wherein said feed stock additionally contains a minor amount of olens not removable by fractionation and solvent extraction, whereby said olens are present in said second bottoms fraction, and wherein said second bottoms fraction is subsequently treated for the removal of said olefms.

3. A method for recovering benzene from a hydrocarbon feed stock comprising a mixture of benzene with six and seven carbon atom parainic and naphthenic hydrocarbons, said feed stock boiling within the range of about to about 220 F., which comprises the steps of fractionating said feed stock to provide an overheads fraction boiling below about F., a lirst distillate fraction boiling in the range between about 145 and about F., a second distillate fraction boiling in the range between about 170 and about 180 F. and a first bottoms fraction boiling above about F., countercurrently contacting said first distillate fraction in an extraction zone solely with about 11/2 to 3 Volumes of liquefied sulfur dioxide per volume of first distillate fraction under conditions to form a rst extract phase and a rst raffinate pbase, dissolving said second distillate fraction in up to about 21/2 volumes of liquefied sulfur dioxide per volume of said second distillate fraction to provide a solution of said distillate fraction in liquefied sulfur dioxide, countercurrently contacting said solution with about 5 to 20 volumes per volume of solution of a wash oil comprising non-aromatic hydrocarbons boiling substantially above about 180 F. under conditions to form a second extract phase and a second raflinate phase, removing sulfur dioxide from said rst and second extract streams and fractionate said first and second extract streams in combination to provide an overheads fraction comprising not more than about 30 volume percent of said combination and a second bottoms fraction consisting of at least about 95 weight percent of benzene, said feed stock containing not more than a minor amount of olens.

4. A method as in claim 3 wherein said feed stock additionally contains a minor amount of olens not removable by fractionation and solvent extraction, whereby said oleiins are present in said second bottoms fraction, and wherein said second bottoms fraction is subsequently treated for the removal of said oleiins.

References Cited in the le of this patent UNITED STATES PATENTS 2,689,819 Shelton et al Sept. 21, 1954 2,724,682 Shelton et al NOV. 22, 1955 2,733,283 Hamner Jan. 3l, 1956 2,758,141 Findlay Aug. 7, 1956 OTHER REFERENCES Petroleum Rener, vol. 30, No. 9, Sept. 1951, pages 237-238. f 

1. A METHOD FOR RECOVERING BENZENE FROM A FEED STOCK COMPRISING A MIXTURE OF BENZENE WITH SIX AND SEVEN CARBON ATOM PARAFFINIC AND NAPHTHENIC HYDROCARBONS WHICH COMPRISES THE STEPS OF FRACTIONATING SAID FEED STOCK TO PROVIDE A FIRST OVERHEADS FRACTION BOILING BELOW ABOUT 145* F. A FIRST DISTILLATE FRACTION BOILING IN THE RANGE BETWEEN ABOUT 145* AND ABOUT 170* F, A SECOND DISTILLATE FRACTION BOILING IN THE RANGE BETWEEN ABOUT 170* AND ABOUT 180* F. AND A FIRST BOTTOMS FRACTION BOILING ABOVE ABOUT 180*F, COUNTERCURRENTLY CONTACTING SAID FIRST DISTILLATE FRACTION SOLELY WITH LIQUEFIED SULFUR DIOXIDE IN AN EXTRACTION ZONE UNDER CONDITIONS TO FORM A FIRST EXTRACT PHASE AND A FIRST RAFFINATE PHASE, DISSOLVING SAID SECOND DISTILLATE FRACTION IN LIQUEFIED SULFUR DIOXIDE, COUNTERCURRENTLY CONTACTING SAID THUS PREPARED SOLUTION OF SAID SECOND DISTILLATE FRACTION WITH A WASH OIL COMPRISING NON-AROMATIC HYDROCARBONS BOILING SUBSTANTIALLY ABOVE ABOUT 180* F. UNDER CONDITIONS TO FORM A SECOND EXTRACT STREAM AND A SECOND RAFFINATE STREAM, REMOVING SULFUR DIOXIDE FROM 